docs: give the Previews Base its own build settings in Deploying

[rqbazan]

Summary

The "Workers Builds: variablelab-www" check failed on every new branch. Workers Builds copies the Previews Base build settings into a new branch's trigger, and that base had no build command. So npx wrangler preview ran with no dist/.

The base is now fixed in the account, not in this repo: PATCH /accounts/{account_id}/builds/workers/{worker_tag}, with production_settings unchanged byte for byte.

 previews_base_config
-  build_command: ""
+  build_command: "pnpm exec astro build"
-  environment_variables: {}
+  environment_variables: { NODE_VERSION: "24" }
   deploy_command: "npx wrangler preview"

This PR updates README.md#deploying to match:

• It lists both sets of build settings, Production and Previews Base.
• It corrects two claims. wrangler preview does run build.command, which stays out of wrangler.jsonc so a build doesn't run Astro twice. And Workers Builds reads neither mise.toml nor mise.lock.
• It separates the build Previews Base from the runtime one.
• It shows how a branch with a / becomes its Preview URL.

Evidence

• Before (ci: add Dependabot security updates and a weekly dependency audit #6, ci/deps-security): trigger build_command: ""

  Executing user deploy command: npx wrangler preview
  ✘ [ERROR] The directory specified by the "assets.directory" field in your configuration file does not exist: /opt/buildhome/repo/dist
  

  After (throwaway ci/preview-base-test, pushed after the PATCH, then deleted): trigger build_command: "pnpm exec astro build", NODE_VERSION=24

  Installing nodejs 24.22.0
  Executing user build command: pnpm exec astro build
  Preview URL: https://ci-preview-base-test-variablelab-www.raquirozbazan.workers.dev   → 200
  

  This PR's own Workers Builds check passed the same way.
• Claims the README now makes, tested on a throwaway branch:
  • With build.command in wrangler.jsonc, wrangler preview logged [custom build] Running: pnpm exec astro build.
  • With mise pinned to node = "24.20.0", Workers Builds still detected nodejs@24.21.0, the image's default.
  • Deleting a branch deleted its trigger and its Preview within seconds.

Merge Danger

Door: two-way

Docs only. You can revert the account change with the same PATCH: set build_command back to "" and environment_variables to {}.

Blast Radius: none

Production deploys are unchanged. Branches pushed before the PATCH keep their old trigger, but none are open.

🤖 Generated with Claude Code

https://claude.ai/code/session_01DbUmufsTzLnGp4dve7NYP7

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Latest commit: 19ad516

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[cloudflare-workers-and-pages]

🚀 Deploying Preview to Cloudflare 🚀

Preview URL: https://docs-preview-builds-variablelab-www.raquirozbazan.workers.dev (commit 19ad516)

This URL reflects your latest Preview deployment

Preview Deployments by commit

Status	Deployment URL	Commit	Updated (UTC)	See this deployment's details
Build: Success ✅ Deployment: Success ✅ View logs ↗	https://27bc857e-variablelab-www.raquirozbazan.workers.dev	19ad516	2026-10-18T00:06:28.303Z	Visit the dashboard ↗